dbx 3BX III, Руководство по обслуживанию

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Model 3BX III Service Manual
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Finally, the signal passes to the switching circuitry. The switching
allows the 3BX III signal path (a) to come either before or after a tape
deck plugged into the tape jacks of the 3BX III, (b) to receive its
signal from either the tape deck or the source, and (c) to bypass the
circuitry.
CONTROL-VOLTAGE (CV) PATH
The 3BX III has two main purposes: first, to make loud signals louder
while making soft signals softer (upward and downward expansion), and
second, to emphasize musical transients (impact restoration). The three
rms detectors translate the signal level in each of the three bands into
voltages (at dc or nearly so) that indicate how loud the input signal is
in each of these bands. These voltages can then be processed and used to
control the gain of the VCAs in the 3BX III to accomplish its two
purposes. Choosing the correct time constants for the rms detectors in
the first place is critical to doing this job right. Then the rms-
detector signals must be processed to find the transients and produce
signals suitable for increasing the music’s impact. All of this
detecting and processing takes place in the CV-path section of the
3BX III.
Refer to Fig. 3, a block diagram of the CV path. The audio signals at
the outputs of each of the signal-path filters are connected to the
inputs of three rms-level detectors, one for each band (U707 is the low-
band detector, U708 the mid-band, U709 the high-band). For each band,
the left- and right-channel signals are summed at pin 1 of the rms-
detector IC. For a detailed explanation of this part, refer to the
booklet on the rms-detector IC.
Figure 3, Control-Voltage Path